Agent for forming coating for narrowing patterns and method for forming fine pattern using the same

ABSTRACT

It is disclosed an over-coating agent for forming fine patterns which is applied to cover a substrate having photoresist patterns thereon and allowed to shrink under heat so that the spacing between the adjacent photoresist patterns is lessened, further characterized by containing a water-soluble polymer and a surfactant. Also disclosed is a method of forming fine-line patterns using the over-coating agent. According to the invention, one can obtain fine-line patterns which exhibit good profiles while satisfying the characteristics required of semiconductor devices, being excellent in controlling the dimension of patterns.

TECHNICAL FIELD

[0001] This invention relates to an over-coating agent for forming finepatterns in the field of photolithographic technology and a method offorming fine-line patterns using such agent. More particularly, theinvention relates to an over-coating agent for forming or definingfine-line patterns, such as hole patterns and trench patterns, that canmeet today's requirements for higher packing densities and smaller sizesof semiconductor devices.

BACKGROUND ART

[0002] In the manufacture of electronic components such as semiconductordevices and liquid-crystal devices, there is employed thephotolithographic technology which, in order to perform a treatment suchas etching on the substrate, first forms a film (photoresist layer) overthe substrate using a so-called radiation-sensitive photoresist which issensitive to activating radiations, then performs exposure of the filmby selective illumination with an activating radiation, performsdevelopment to dissolve away the photoresist layer selectively to forman image pattern (photoresist pattern), and forms a variety of patternsincluding contact providing patterns such as a hole pattern and a trenchpattern using the photoresist pattern as a protective layer (maskpattern). photoresist pattern as a protective layer (mask pattern).

[0003] With the recent increase in the need for higher packing densitiesand smaller sizes of semiconductor devices, increasing efforts are beingmade to form sufficiently fine-line patterns and submicron-electronicfabrication capable of forming patterns with linewidths of no more than0.20 μm is currently required. As for the activating light raysnecessary in the formation of mask patterns, short-wavelength radiationssuch as KrF, ArF and F₂ excimer laser beams and electron beams areemployed. Further, active R&D efforts are being made to find photoresistmaterials as mask pattern formers that have physical properties adaptedto those short-wavelength radiations.

[0004] In addition to those approaches for realizingsubmicron-electronic fabrication which are based on photoresistmaterials, active R&D efforts are also being made on the basis ofpattern forming method with a view to finding a technology that canprovide higher resolutions than those possessed by photoresistmaterials.

[0005] For example, JP-5-166717A discloses a method of forming finepatterns which comprises the steps of defining patterns(=photoresist−uncovered patterns) into a pattern-forming resist on asubstrate, then coating over entirely the substrate with a mixinggenerating resist that is to be mixed with said pattern-forming resist,baking the assembly to form a mixing layer on both sidewalls and the topof the pattern-forming resist, and removing the non-mixing portions ofsaid mixing generating resist such that the feature size of thephotoresist-uncovered pattern is reduced by an amount comparable to thedimension of said mixing layer. JP-5-241348 discloses a pattern formingmethod comprising the steps of depositing a resin, which becomesinsoluble in the presence of an acid, on a substrate having formedthereon a resist pattern containing an acid generator, heat treating theassembly so that the acid is diffused from the resist pattern into saidresin insoluble in the presence of an acid to form a given thickness ofinsolubilized portion of the resist near the interface between the resinand the resist pattern, and developing the resist to remove the resinportion through which no acid has been diffused, thereby ensuring thatthe feature size of the pattern is reduced by an amount comparable tothe dimension of said given thickness.

[0006] However, in these methods, it is difficult to control thethickness of layers to be formed on the sidewalls of resist patterns. Inaddition, the in-plane heat dependency of wafers is as great as ten-oddnanometers per degree Celsius, so it is extremely difficult to keep thein-plane uniformity of wafers by means of the heater employed in currentfabrication of semiconductor devices and this leads to the problem ofoccurrence of significant variations in pattern dimensions.

[0007] Another approach known to be capable of reducing patterndimensions is by fluidizing resist patterns through heat treatment andthe like. For example, JP-1-307228A discloses a method comprising thesteps of forming a resist pattern on a substrate and applying heattreatment to deform the cross-sectional shape of the resist pattern,thereby defining a fine pattern. In addition, JP-4-364021A discloses amethod comprising the steps of forming a resist pattern and heating itto fluidize the resist pattern, thereby changing the dimensions of itsresist pattern to form or define a fine-line pattern.

[0008] In these methods, the wafer's in-plane heat dependency is only afew nanometers per degree Celsius and is not very problematic. On theother hand, it is difficult to control the resist deformation andfluidizing on account of heat treatment, so it is not easy to provide auniform resist pattern in a wafer's plane.

[0009] An evolved version of those methods is disclosed in JP-7-45510Aand it comprises the steps of forming a resist pattern on a substrate,forming a stopper resin on the substrate to prevent excessive thermalfluidizing of the resist pattern, then applying heat treatment tofluidize the resist so as to change the dimensions of its pattern, andthereafter removing the stopper resin to form or define a fine-linepattern. As the stopper resin, specifically, polyvinyl alcohol isemployed. However, polyvinyl alcohol is not highly soluble in water andcannot be readily removed completely by washing with water, introducingdifficulty in forming a pattern of good profile. The pattern formed isnot completely satisfactory in terms of stability over time. Inaddition, polyvinyl alcohol cannot be applied efficiently by coating.Because of these and other problems, the method disclosed in JP-7-45510has yet to be adopted commercially.

[0010] Further, microfoaming is a problem that currently affects theapplication of a coating material to a substrate having a photoresistpattern. Since this problem is said to have something to do with thegeneration of pattern defects, commonly referred to simply as defects,coating materials are required that can also solve the problem ofdefects.

[0011] JP 2001-281886A discloses a method comprising the steps ofcovering a surface of a resist pattern with an acidic film made of aresist pattern size reducing material containing a water-soluble resin,rendering the surface layer of the resist pattern alkali-soluble, thenremoving said surface layer and the acidic film with an alkalinesolution to reduce the feature size of the resist pattern.JP-2002-184673A discloses a method comprising the steps of forming aresist pattern on a substrate, then forming a film containing awater-soluble film forming component on said resist pattern, heattreating said resist pattern and film, and immersing the assembly in anaqueous solution of tetramethylammonium hydroxide, thereby forming afine-line resist pattern without involving a dry etching step. However,both methods are simply directed to reducing the size of resist tracepatterns themselves and therefore are totally different from the presentinvention in object.

DISCLOSURE OF INVENTION

[0012] An object of the present invention is to provide an over-coatingagent for forming fine patterns. It has high ability to control patterndimensions and provides fine-line patterns that have a satisfactoryprofile and satisfy the characteristics required of semiconductordevices. Another object of the invention is to provide a method offorming fine trace patterns using the over-coating agent.

[0013] In order to attain the first object, the present inventionprovides an over-coating agent for forming fine patterns which isapplied to cover a substrate having photoresist patterns thereon andallowed to shrink under heat so that the spacing between the adjacentphotoresist patterns is lessened, further characterized by containing awater-soluble polymer and a surfactant.

[0014] In a preferred embodiment, the surfactant is at least one memberselected from the group consisting of N-alkylpyrrolidones, quaternaryammonium salts and phosphate esters of polyoxyethylene.

[0015] In order to attain the second object, the present inventionprovides a method of forming fine patterns comprising the steps ofcovering a substrate having thereon photoresist patterns with theabove-described over-coating agent for forming fine patterns, thenapplying heat treatment to shrink the applied over-coating agent underthe action of heat so that the spacing between the adjacent photoresistpatterns is lessened, and subsequently removing the applied film of theover-coating agent.

[0016] In a preferred embodiment, the heat treatment is performed byheating the assembly at a temperature that does not cause thermalfluidizing of the photoresist patterns on the substrate.

BEST MODE FOR CARRYING OUT THE INVENTION

[0017] The over-coating agent of the invention for forming fine featuresof patterns is applied to cover a substrate, having photoresist patterns(mask patterns) thereon, including patterns typified by hole patterns ortrench patterns, each of these patterns are defined by spacing betweenthe adjacent photoresist patterns (mask patterns). Upon heating, theapplied film of over-coating agent shrinks to increase the width of eachof the photoresist patterns, thereby narrowing or lessening holepatterns or trench patterns as defined by spacing between the adjacentphotoresist patterns and, thereafter, the applied film is removedcompletely to form or define fine patterns.

[0018] The over-coating agent of the invention for forming fine patternscontains a water-soluble polymer and a surfactant.

[0019] The water-soluble polymer may be any polymer that can dissolve inwater at room temperature and various types may be employed withoutparticular limitation; preferred examples include acrylic polymers,vinyl polymers, cellulosic derivatives, alkylene glycol polymers, ureapolymers, melamine polymers, epoxy polymers and amide polymers.

[0020] Exemplary acrylic polymers include polymers and copolymers havingmonomeric components, such as acrylic acid, methyl acrylate, methacrylicacid, methyl methacrylate, N,N-dimethylacrylamide,N,N-dimethylaminopropylmethacrylamide,N,N-dimethylaminopropylacrylamide, N-methylacrylamide, diacetoneacrylamide, N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethylmethacrylate, N,N-dimethylaminoethyl acrylate, acryloylmorpholine, etc.

[0021] Exemplary vinyl monomers include polymers and copolymers havingmonomeric components, such as N-vinylpyrrolidone, vinyl imidazolidinone,vinyl acetate, etc.

[0022] Exemplary cellulosic derivatives include hydroxypropylmethylcellulose phthalate, hydroxypropylmethyl cellulose acetate phthalate,hydroxypropylmethyl cellulose hexahydrophthalate, hydroxypropylmethylcellulose acetate succinate, hydroxypropylmethyl cellulose,hydroxypropyl cellulose, hydroxyethyl cellulose, cellulose acetatehexahydrophthalate, carboxymethyl cellulose, ethyl cellulose,methylcellulose, etc.

[0023] Exemplary alkylene glycol polymers include addition polymers andcopolymers of ethylene glycol, propylene glycol, etc.

[0024] Exemplary urea polymers include those having methylolurea,dimethylolurea, ethyleneurea, etc. as components.

[0025] Exemplary melamine polymers include those havingmethoxymethylated melamine, methoxymethylated isobutoxymethylatedmelamine, methoxyethylated melamine, etc. as components.

[0026] Among epoxy polymers and amide polymers, those which arewater-soluble may also be employed.

[0027] It is particularly preferred to employ at least one memberselected from the group consisting of alkylene glycol polymers,cellulosic derivatives, vinyl polymers and acrylic polymers. Acrylicpolymers are most preferred since they provide ease in pH adjustment.Copolymers comprising acrylic polymers and water-soluble polymers otherthan acrylic polymers are also preferred since during heat treatment,the efficiency of shrinking the spacing between the adjacent photoresistpatterns (mask patterns) can be increased while maintaining the shape ofthe photoresist pattern. The water-soluble polymers can be employedeither singly or in combination.

[0028] When water-soluble polymers are used as copolymers, theproportions of the components are not limited to any particular values.However, if stability over time is important, the proportion of theacrylic polymer is preferably adjusted to be larger than those of otherbuilding polymers. Other than by using excessive amounts of the acrylicpolymer, better stability over time can also be obtained by addingacidic compounds such as p-toluenesulfonic acid anddodecylbenzenesulfonic acid.

[0029] The surfactant is not limited to any particular types, exceptthat when it is added to the water-soluble polymer, it must exhibitcertain characteristics such as high solubility, non-formation of asuspension and miscibility with the polymer component. The use of suchsurfactants that satisfy these characteristics can effectively preventthe generation of defects that has been problems in conventionalmethods, which is considered to be pertinent to microfoaming uponapplying over-coating materials on the substrate.

[0030] Suitable surfactants include N-alkylpyrrolidones, quaternaryammonium salts and phosphate esters of polyoxyethylene.

[0031] N-alkylpyrrolidones as surfactant are preferably represented bythe following general formula (I):

[0032] where R₁ is an alkyl group having at least 6 carbon atoms.

[0033] Specific examples of N-alkylpyrrolidones as surfactant includeN-hexyl-2-pyrrolidone, N-heptyl-2-pyrrolidone, N-octyl-2-pyrrolidone,N-nonyl-2-pyrrolidone, N-decyl-2-pyrrolidone, N-undecyl-2-pyrrolidone,N-dodecyl-2-pyrrolidone, N-tridecyl-2-pyrrolidone,N-tetradecyl-2-pyrrolidone, N-pentadecyl-2-pyrrolidone,N-hexadecyl-2-pyrrolidone, N-heptadecyl-2-pyrrolidone andN-octadecyl-2-pyrrolidone. Among these, N-octyl-2-pyrrolidone(“SURFADONE LP 100” of ISP Inc.) is preferably used.

[0034] Quaternary ammonium salts as surfactant are preferablyrepresented by the following general formula (II):

[0035] where R₂, R₃, R₄ and R₅ are each independently an alkyl group ora hydroxyalkyl group (provided that at least one of them is an alkyl orhydroxyalkyl group having not less than 6 carbon atoms); X⁻ is ahydroxide ion or a halogenide ion.

[0036] Specific examples of quaternary ammonium salts as surfactantinclude dodecyltrimethylammonium hydroxide, tridecyltrimethylammoniumhydroxide, tetradecyltrimethylammonium hydroxide,pentadecyltrimethylammonium hydroxide, hexadecyltrimethylammoniumhydroxide, heptadecyltrimethylammonium hydroxide andoctadecyltrimethylammonium hydroxide. Among these,hexadecyltrimethylammonium hydroxide is preferably used.

[0037] Phosphate esters of polyoxyethylene are preferably represented bythe following general formula (III):

[0038] where R₆ is an alkyl or alkylaryl group having 1-10 carbon atoms;R₇ is a hydrogen atom or (CH₂CH₂O)R₆ (where R₆ is as defined above); nis an integer of 1-20.

[0039] To mention specific examples, phosphate esters of polyoxyethylenethat can be used as surfactants are commercially available under tradenames “PLYSURF A212E” and “PLYSURF A210G” from Dai-ichi Kogyo SeiyakuCo., Ltd.

[0040] Among these surfactants, phosphate esters of phosphate esters ofpolyoxyethylene are preferable employed in view of suppressing thegeneration of defects.

[0041] The amount of the surfactant is preferably about 0.1-10 mass %,more preferably about 0.2-2 mass %, of the over-coating agent (in termsof solids content). If the amount of the surfactant is beyond theaforementioned ranges, it may cause the variations in the percentshrinkage of patterns, potentially depending on the wafer's in-planeuniformity which is caused by the deterioration of coating property, andalso may cause the occurrence of defects that are considered to bepertinent to microfoaming on the over-coating material.

[0042] For special purposes such as preventing the generation ofimpurities and pH adjustment, the over-coating agent for forming finepatters of the present invention may additionally contain water-solubleamines.

[0043] Exemplary water-soluble amines include amines having pKa (aciddissociation constant) values of 7.5-13 in aqueous solution at 25° C.Specific examples include the following: alkanolamines, such asmonoethanolamine, diethanolamine, triethanolamine,2-(2-aminoethoxy)ethanol, N,N-dimethylethanolamine,N,N-diethylethanolamine, N,N-dibutylethanolamine, N-methylethanolamine,N-ethylethanolamine, N-butylethanolamine, N-methyldiethanolamine,monoisopropanolamine, diisopropanolamine and triisopropanolamine;polyalkylenepolyamines, such as diethylenetriamine,triethylenetetramine, propylenediamine, N,N-diethylethylenediamine,1,4-butanediamine, N-ethylethylenediamine, 1,2-propanediamine,1,3-propanediamine and 1,6-hexanediamine; aliphatic amines, such astriethylamine, 2-ethyl-hexylamine, dioctylamine, tributylamine,tripropylamine, triallylamine, heptylamine and cyclohexylamine; aromaticamines such as benzylamine and diphenylamine; and cyclic amines, such aspiperazine, N-methyl-piperazine and hydroxyethylpiperazine. Preferredwater-soluble amines are those having boiling points of 140° C. (760mmHg) and above, as exemplified by monoethanolamine and triethanolamine.

[0044] If the water-soluble amine is to be added, it is preferablyincorporated in an amount of about 0.1-30 mass %, more preferably about2-15 mass %, of the over-coating agent (in terms of solids content). Ifthe water-soluble amine is incorporated in an amount of less than 0.1mass %, the coating fluid may deteriorate over time. If thewater-soluble amine is incorporated in an amount exceeding 30 mass %,the photoresist pattern being formed may deteriorate in shape.

[0045] For such purposes as reducing the dimensions of patterns andcontrolling the occurrence of defects, the over-coating agent forforming fine patterns may further optionally contain non-amine based,water-soluble organic solvents.

[0046] As such non-amine based, water-soluble organic solvents, anynon-amine based organic solvents that can mix with water may be employedand they may be exemplified by the following: sulfoxides, such asdimethyl sulfoxide; sulfones, such as dimethylsulfone, diethylsulfone,bis(2-hydroxyethyl)sulfone and tetramethylenesulfone; amides, such asN,N-dimethylformamide, N-methylformamide, N,N-dimethylacetamide,N-methylacetamine and N,N-diethylacetamide; lactams, such asN-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-propyl-2-pyrrolidone,N-hydroxymethyl-2-pyrrolidone and N-hydroxyethyl-2-pyrrolidone;imidazolidinones, such as 1,3-dimethyl-2-imidazolidinone,1,3-diethyl-2-imidazolidinone and 1,3-diisopropyl-2-imidazolidinone; andpolyhydric alcohols and derivatives thereof, such as ethylene glycol,ethylene glycol monomethyl ether, ethylene glycol monoethyl ether,ethylene glycol monobuthyl ether, ethylene glycol monomethyl etheracetate, ethylene glycol monoethyl ether acetate, diethylene glycol,diethylene glycol monomethyl ether, diethylene glycol monoethyl ether,diethylene glycol monobuthyl ether, propylene glycol, propylene glycolmonomethyl ether, glycerol, 1,2-butylene glycol, 1,3-butylene glycol and2,3-butylene glycol. Among those mentioned above, polyhydric alcoholsand their derivatives are preferred for the purposes of reducing thedimensions of patterns and controlling the occurrence of defects andglycerol is particularly preferred. The non-amine based, water-solubleorganic solvents may be used either singly or in combination.

[0047] If the non-amine based, water-soluble organic solvent is to beadded, it is preferably incorporated in an amount of about 0.1-30 mass%, more preferably about 0.5-15 mass %, of the water-soluble polymer. Ifthe non-amine based, water-soluble organic solvent is incorporated in anamount of less than 0.1 mass %, its defect reducing effect tends todecrease. Beyond 30 mass %, a mixing layer is liable to form at theinterface with the photoresist pattern.

[0048] The over-coating agent of the invention for forming fine patternsis preferably used as an aqueous solution at a concentration of 3-50mass %, more preferably at 5-30 mass %. If the concentration of theaqueous solution is less than 3 mass %, poor coverage of the substratemay result. If the concentration of the aqueous solution exceeds 50 mass%, there is no appreciable improvement in the intended effect thatjustifies the increased concentration and the solution cannot be handledefficiently.

[0049] As already mentioned, the over-coating agent of the invention forforming fine patterns is usually employed as an aqueous solution usingwater as the solvent. A mixed solvent system comprising water and analcoholic solvent may also be employed. Exemplary alcoholic solvents aremonohydric alcohols including methyl alcohol, ethyl alcohol, propylalcohol and isopropyl alcohol. These alcoholic solvents are mixed withwater in amounts not exceeding about 30 mass %.

[0050] The over-coating agent of the invention for forming fine patternshas the advantage of improving resolution beyond the values inherent inphotoresist materials and it can attain wafer's in-plane uniformity byeliminating the pattern variations in the plane of the substrate.Further, the over-coating agent of the invention can form patterns ofgood profile by eliminating the irregularities (roughness) in the shapeof patterns due, for example, to the reflection of fluorescent lightfrom the substrate. Yet another advantage of the over-coating agent isits ability to check the occurrence of defects.

[0051] The method of forming fine-line patterns according to the secondaspect of the invention comprises the steps of covering a substratehaving photoresist patterns thereon with the above-describedover-coating agent for forming fine patterns, then applying heattreatment to shrink the applied over-coating agent under the action ofheat so that the spacing between the adjacent photoresist patterns isreduced, and subsequently removing the applied film of the over-coatingagent.

[0052] The method of preparing the substrate having photoresist patternsthereon is not limited to any particular type and it can be prepared byconventional methods employed in the fabrication of semiconductordevices, liquid-crystal display devices, magnetic heads and microlensarrays. In an exemplary method, a photoresist composition of chemicallyamplifiable or other type is spin- or otherwise coated on a substratesuch as a silicon wafer and dried to form a photoresist layer, which isilluminated with an activating radiation such as ultraviolet,deep-ultraviolet or excimer laser light through a desired mask patternusing a reduction-projection exposure system or subjected to electronbeam photolithography, then heated and developed with a developer suchas an alkaline aqueous solution, typically a 1-10 mass %tetramethylammonium hydroxide (TMAH) aqueous solution, thereby forming aphotoresist pattern on the substrate.

[0053] The photoresist composition serving as a material from whichphotoresist patterns are formed is not limited in any particular way andany common photoresist compositions may be employed including those forexposure to i- or g-lines, those for exposure with an excimer laser(e.g. KrF, ArF or F₂) and those for exposure to EB (electron beams).

[0054] After thusly forming the photoresist pattern as a mask pattern,the over-coating agent for forming fine patterns is applied to coverentirely the substrate. After applying the over-coating agent, thesubstrate may optionally be pre-baked at a temperature of 80-100° C. for30-90 seconds.

[0055] The over-coating agent may be applied by any methods commonlyemployed in the conventional heat flow process. Specifically, an aqueoussolution of the over-coating agent for forming fine patterns is appliedto the substrate by any known application methods including bar coating,roll coating and whirl coating with a spinner.

[0056] In the next step, heat treatment is performed to cause thermalshrinkage of the film of the over-coating agent. Under the resultingforce of thermal shrinkage of the film, the dimensions of thephotoresist pattern in contact with the film will increase by an amountequivalent to the thermal shrinkage of the film and, as the result, thephotoresist pattern widens and accordingly the spacing between theadjacent photoresist patterns lessens. The spacing between the adjacentphotoresist patterns determines the diameter or width of the patterns tobe finally obtained, so the decrease in the spacing between the adjacentphotoresist patterns contributes to reducing the diameter of eachelement of hole patterns or the width of each element of trenchpatterns, eventually leading to the definition of a pattern with smallerfeature sizes.

[0057] The heating temperature is not limited to any particular value aslong as it is high enough to cause thermal shrinkage of the film of theover-coating agent and form or define a fine pattern. Heating ispreferably done at a temperature that will not cause thermal fluidizingof the photoresist pattern. The temperature that will not cause thermalfluidizing of the photoresist pattern is such a temperature that when asubstrate on which the photoresist pattern has been formed but no filmof the over-coating agent has been formed is heated, the photoresistpattern will not experience any dimensional changes (for example,dimensional changes due to spontaneously fluidized deforming).Performing a heat treatment under such temperature conditions is veryeffective for various reasons, e.g. a fine-line pattern of good profilecan be formed more efficiently and the duty ratio in the plane of awafer, or the dependency on the spacing between photoresist patterns inthe plane of a wafer, can be reduced. Considering the softening pointsof a variety of photoresist compositions employed in currentphotolithographic techniques, the preferred heat treatment is usuallyperformed within a temperature range of about 80-160° C. for 30-90seconds, provided that the temperature is not high enough to causethermal fluidizing of the photoresist.

[0058] The thickness of the film of the over-coating agent for theformation of fine-line patterns is preferably just comparable to theheight of the photoresist pattern or high enough to cover it.

[0059] In the subsequent step, the remaining film of the over-coatingagent on the patterns is removed by washing with an aqueous solvent,preferably pure water, for 10-60 seconds. Prior to washing with water,rinsing may optionally be performed with an aqueous solution of alkali(e.g. tetramethylammonium hydroxide (TMAH) or choline). The over-coatingagent of the present invention is easy to remove by washing with waterand it can be completely removed from the substrate and the photoresistpattern.

[0060] As a result, each pattern on the substrate has a smaller featuresize because each pattern is defined by the narrowed spacing between theadjacent widened photoresist patterns.

[0061] The fine-line pattern thus formed using the over-coating agent ofthe present invention has a pattern size smaller than the resolutionlimit attainable by the conventional methods. In addition, it has a goodenough profile and physical properties that can fully satisfy thecharacteristics required of semiconductor devices.

[0062] The technical field of the present invention is not limited tothe semiconductor industry and it can be employed in a wide range ofapplications including the fabrication of liquid-crystal displaydevices, the production of magnetic heads and even the manufacture ofmicrolens arrays.

EXAMPLES

[0063] The following examples are provided for further illustrating thepresent invention but are in no way to be taken as limiting. Unlessotherwise noted, all amounts of ingredients are expressed in mass %.

Example 1

[0064] A substrate was whirl coated with a positive-acting photoresistTDUR-PO36PM (product of Tokyo Ohka Kogyo Co., Ltd.) and baked at 80° C.for 90 seconds to form a photoresist layer in a thickness of 0.48 μm.

[0065] The photoresist layer was exposed with a KrF excimer laserexposure unit (FPA-3000 EX3 of Canon Inc.), subjected to heat treatmentat 120° C. for 90 seconds and developed with an aqueous solution of 2.38mass % TMAH (tetramethylammonium hydroxide) to form photoresist patternswhich defined hole patterns with an each diameter of 180 nm (i.e., thespacing between the photoresist patterns was 180 nm).

[0066] A copolymer of acrylic acid and vinylpyrrolidone [10 g; acrylicacid/vinylpyrrolidone=2:1 (by weight)] and “SURFADONE LP 100”, productof ISP Inc., as N-alkylpyrrolidone surfactant (0.02 g) were dissolved inwater to prepare an over-coating agent having the overall solids contentadjusted to 8.0 mass %.

[0067] Then thusly prepared over-coating agent was applied onto thesubstrate including the hole patterns and subjected to heat treatment at116° C. for 60 seconds. Subsequently, the over-coating agent was removedusing pure water at 23° C. The each diameter of the hole patterns wasreduced to about 160 nm. In addition, wafer's in-plane uniformity wasgood, and the variations in flow-rates were suppressed. The generationof defects, which is considered to be caused by microfoaming uponapplying the coating, was suppressed. Furthermore, the thus obtainedpatterns had a good profile.

Example 2

[0068] Photoresist patterns were formed in the same manner as describedin Example 1, which defined hole patterns with an each diameter of 180nm (i.e., the spacing between the photoresist patterns was 180 nm).

[0069] A copolymer of acrylic acid and vinylpyrrolidone [10 g; acrylicacid/vinylpyrrolidone=2:1 (by weight)], triethanolamine (0.9 g) and“SURFADONE LP 100”, product of ISP Inc., as N-alkylpyrrolidonesurfactant (0.02 g) were dissolved in water to prepare an over-coatingagent having the overall solids content adjusted to 8.0 mass %.

[0070] Then thusly prepared over-coating agent was applied onto thesubstrate including the hole patterns and subjected to heat treatment at116° C. for 60 seconds. Subsequently, the over-coating agent was removedusing pure water at 23° C. The each diameter of the hole patterns wasreduced to about 160 nm. In addition, wafer's in-plane uniformity wasgood, and the variations in flow-rates were suppressed. The generationof defects, which is considered to be caused by microfoaming uponapplying the coating, was suppressed. Furthermore, the thus obtainedpatterns had a good profile.

Example 3

[0071] Photoresist patterns were formed in the same manner as describedin Example 1, which defined trench patterns with an each pattern-widthof 180 nm (i.e., the spacing between the photoresist patterns was 180nm).

[0072] A copolymer of acrylic acid and vinylpyrrolidone [10 g; acrylicacid/vinylpyrrolidone=2:1 (by weight)], triethanolamine (0.9 g) and aquaternary ammonium salt surfactant [0.02 g;HDTMAH(=hexadecyltrimethylammonium hydroxide); product of Wako PureChemical Industries, Ltd.] were dissolved in water to prepare anover-coating agent having the overall solids content adjusted to 8.0mass %.

[0073] Then thusly prepared over-coating agent was applied onto thesubstrate including the trench patterns and subjected to heat treatmentat 116° C. for 60 seconds. Subsequently, the over-coating agent wasremoved using pure water at 23° C. The each pattern-width of trenchpatterns was reduced to about 160 nm. In addition, wafer's in-planeuniformity was good, and the variations in flow-rates were suppressed.The generation of defects, which is considered to be caused bymicrofoaming upon applying the coating, was suppressed. Furthermore, thethus obtained patterns had a good profile.

Example 4

[0074] Photoresist patterns were formed in the same manner as describedin Example 1, which defined hole patterns with an each diameter of 181.5nm (i.e., the spacing between the photoresist patterns was 181.5 nm).

[0075] A copolymer of acrylic acid and vinylpyrrolidone [6.93 g; acrylicacid/vinylpyrrolidone=2:1 (by weight)] and “PLYSURF A210G”, product ofDai-ichi Kogyo Seiyaku Co., Ltd., as a polyoxyethylene phosphate esterbased surfactant (0.07 g) were dissolved in water (93 g) to prepare anover-coating agent.

[0076] Then thusly prepared over-coating agent was applied onto thesubstrate including the hole patterns and subjected to heat treatment at120° C. for 60 seconds. Subsequently, the over-coating agent was removedusing pure water at 23° C. The each diameter of the hole patterns wasreduced to 161.4 nm. In addition, wafer's in-plane uniformity was good,and the variations in flow-rates were suppressed. The generation ofdefects, which is considered to be caused by microfoaming upon applyingthe coating, was effectively suppressed: the numbers of the defectsgenerated in Example 4 were about 15% of the numbers of the defectsgenerated in Examples 1-3. Furthermore, the thus obtained patterns had agood profile.

Example 5

[0077] Photoresist patterns were formed in the same manner as describedin Example 1, which defined hole patterns with an each diameter of 181.5nm (i.e., the spacing between the photoresist patterns was 181.5 nm).

[0078] A copolymer of acrylic acid and vinylpyrrolidone [6.73 g; acrylicacid/vinylpyrrolidone=2:1 (by weight)], “PLYSURF A210G”, product ofDai-ichi Kogyo Seiyaku Co., Ltd., as a polyoxyethylene phosphate esterbased surfactant (0.07 g) and glycerol (0.20 g) were dissolved in water(93 g) to prepare an over-coating agent. Then thusly preparedover-coating agent was applied onto the substrate including the holepatterns and subjected to heat treatment at 120° C. for 60 seconds.Subsequently, the over-coating agent was removed using pure water at 23°C. The each diameter of the hole patterns was reduced to 160.2 nm. Inaddition, wafer's in-plane uniformity was good, and the variations inflow-rates were suppressed. The numbers of the defects caused bymicrofoaming generated in Example 5 were nearly zero. Furthermore, thethus obtained patterns had a good profile.

Example 6

[0079] Photoresist patterns were formed in the same manner as describedin Example 1, which defined hole patterns with an each diameter of 181.5nm (i.e., the spacing between the photoresist patterns was 181.5 nm).

[0080] A copolymer of acrylic acid and vinylpyrrolidone [6.73 g; acrylicacid/vinylpyrrolidone=2:1 (by weight)], “PLYSURF A210G”, product ofDai-ichi Kogyo Seiyaku Co., Ltd., as a polyoxyethylene phosphate esterbased surfactant (0.07 g) and propylene glycol monomethyl ether (0.20 g)were dissolved in water (93 g) to prepare an over-coating agent. Thenthusly prepared over-coating agent was applied onto the substrateincluding the hole patterns and subjected to heat treatment at 120° C.for 60 seconds. Subsequently, the over-coating agent was removed usingpure water at 23° C. The each diameter of the hole patterns was reducedto 160.2 nm. In addition, wafer's in-plane uniformity was good, and thevariations in flow-rates were reduced. The numbers of the defects causedby microfoaming occurred in Example 6 were nearly zero. Furthermore, thethus obtained patterns had a good profile.

Comparative Example 1

[0081] Photoresist patterns were formed in the same manner as describedin Example 1, which defined trench patterns with an each pattern-widthof 180 nm (i.e., the spacing between the photoresist patterns was 180nm). A copolymer of acrylic acid and vinylpyrrolidone [10 g; acrylicacid/vinylpyrrolidone=2:1 (by weight)] was dissolved in water to preparean over-coating agent having the overall solids content adjusted to 8.0mass %.

[0082] Then thusly prepared over-coating agent was applied onto thesubstrate including the trench patterns and subjected to heat treatmentat 116° C. for 60 seconds. Subsequently, the over-coating agent wasremoved using pure water at 23° C. The each pattern-width of trenchpatterns was reduced to about 160 nm. However, the variations inflow-rates were occurred due to wafer's in-plane non-uniformity, whichis caused by the deterioration of coating properties. Furthermore,defects that were considered to be caused by microfoaming upon applyingthe coating were observed.

INDUSTRIAL APPLICABILITY

[0083] As described above in detail, according to the present inventionsof the over-coating agent for forming fine-line patterns and the methodof forming fine-line patterns using the agent, one can obtain fine-linepatterns which exhibits a good profile while satisfying thecharacteristics required of semiconductor devices, being excellent inremoving the applied film of the over-coating agent.

1. An over-coating agent for forming fine patterns which is applied tocover a substrate having photoresist patterns thereon and allowed toshrink under heat so that the spacing between the adjacent photoresistpatterns is lessened, further characterized by containing awater-soluble polymer and a surfactant.
 2. The over-coating agent forforming fine patterns according to claim 1, wherein the surfactant is atleast one member selected from the group consisting ofN-alkylpyrrolidones, quaternary ammonium salts and phosphate esters ofpolyoxyethylene.
 3. The over-coating agent for forming fine patternsaccording to claim 1, which contains 0.1-10 mass % of the surfactant inthe over-coating agent (as solids).
 4. The over-coating agent forforming fine patterns according to claim 1, wherein the water-solublepolymer is at least one member selected from the group consisting ofalkylene glycolic polymers, cellulosic derivatives, vinyl polymers,acrylic polymers, urea polymers, epoxy polymers, melamine polymers andamide polymers.
 5. The over-coating agent for forming fine patternsaccording to claim 1, wherein the water-soluble polymer is at least onemember selected from the group consisting of alkylene glycolic polymers,cellulosic derivatives, vinyl polymers and acrylic polymers.
 6. Theover-coating agent for forming fine patterns according to claim 1, whichis an aqueous solution having a concentration of 3-50 mass %.
 7. Amethod of forming fine patterns comprising the steps of covering asubstrate having thereon photoresist patterns with the over-coatingagent for forming fine patterns of claim 1, then applying heat treatmentto shrink the applied over-coating agent under the action of heat sothat the spacing between the adjacent photoresist patterns is lessened,and subsequently removing the applied film of the over-coating agent. 8.The method of forming fine patterns according to claim 7, wherein theheat treatment is performed by heating the substrate at a temperaturethat does not cause thermal fluidizing of the photoresist patterns onthe substrate.
 9. The method of forming fine patterns according to claim7, wherein the applied film of the over-coating agent is removed withwater.